1. Field of the Invention
The present invention relates to an electrode plate unit and a battery using the same.
2. Description of the Prior Art
In recent years, secondary batteries are becoming used for various applications. In particular, the application as a driving source of an electric car is to be increased in the future under circumstances in which global environmental protection and effective use of energy resources increasingly have been demanded. With such a variation of applications, the further improvement of the battery property and reliability of a secondary battery have been required.
FIG. 14 shows a conventional secondary battery. In this structure, a battery case 51 housing a group of electrode plates 52 and electrolyte is closed by a lid 57 provided with a safety valve 56. As shown in FIG. 15, the group of electrode plates 52 has a structure in which a plurality of positive electrode plates 61 and a plurality of negative electrode plates 62 are laminated alternately via separators 63. The positive electrode plate 61 and the negative electrode plate 62 are formed by filling a substrate with an active material. As shown in FIG. 14, a lead 53 is led out of the positive electrode plate and connected to the positive electrode terminal 54 provided on the lid 57. Similarly, a lead is led out of the negative electrode plate and connected to the negative electrode terminal 55 provided on the lid 57.
Substrates forming each electrode are produced by cutting out a metal plate. Since a punched metal is used for a substrate for the negative electrode plate, little flashing is formed due to the cutting. On the other hand, when a foam metal is used for a substrate for the positive electrode plate, fibrous flashing is likely to be formed due to the cutting work. Therefore, as shown in FIG. 15, there has been a problem in that a flashing 61a that occurs on the end portion of the positive electrode plate 61 passes through the separator 63 and is brought into contact with the negative electrode 62, thereby causing an internal short circuit between the positive and negative electrodes.
Furthermore, in the above-mentioned conventional secondary battery, there is a problem in that since a side face of the group of electrode plates is exposed, when the group of electrode plates is inserted into the battery case for producing a battery, the electrode plate touches the wall surface of the battery case and may be damaged. One possible example of a structure of the secondary battery proposed in order to avoid such a problem is a structure in which an electrode plate unit in which a positive electrode collector plate is connected to one side of the group of electrode plates and a negative electrode collector plate is connected to another side of the group of electrode plates is housed in a battery case together with electrolyte, and both electrode collector plates are connected to a positive electrode terminal and a negative electrode terminal, respectively. According to this electrode plate unit, since the side face of the group of electrode plates is covered with the collector plate, it is possible to reduce the damage to the electrode plate when the group of electrode plates is inserted into the battery case. In such an electrode plate unit, the group of electrode plates and the collector plate can be connected by welding. By providing the welding places in several places, it is possible to improve the connection strength and collecting efficiency. However, further improvement of the connecting strength between the group of electrode plates and the collector plate and the collecting efficiency are required.
It is a first object of the present invention to provide an electrode plate unit capable of suppressing the internal short circuit caused by flashing that is formed in the end portion of the positive electrode plate and a highly reliable battery using the same. Furthermore, it is a second object of the present invention to provide an electrode plate unit that improves the connecting strength between a group of electrode plates and a collector plate connected to the side face of the group of electrode plates and the collecting efficiency, and a highly reliable battery using the same.
A first electrode plate unit of the present invention includes a group of electrode plates in which a plurality of positive electrode plates and a plurality of negative electrode plates are laminated alternately via separators, a positive electrode collector plate being connected to one side face of the group of electrode plates for connection to the positive electrode plates, and a negative electrode collector plate being connected to another side face of the group of electrode plates for connection to the negative electrode plates, wherein the edge portion of the positive electrode plate is protruded from the edge portion of the negative electrode plate on the entire side face of the group of electrode plates excluding the side face to which the negative electrode collector plates are connected.
According to such an electrode plate unit, even if a flashing is formed on an edge of the positive electrode plate, the flashing is not brought into contact with the negative electrode. Therefore, it is possible to suppress the short circuit between the positive and negative electrodes due to the flashing on the positive electrode. Moreover, the xe2x80x9cside facexe2x80x9d in the group of electrode plates denotes a face parallel to the direction in which the electrode plates are laminated.
It is preferable in the first electrode plate unit that each of the positive electrode plate and the negative electrode plate has positioning holes formed on the edge portion of the side to which the positive electrode collector plate or the negative electrode collector plate is connected.
It is preferable in the first electrode plate unit that each of the positive electrode plate and the negative electrode plate has an electrode portion filled with an active material and a lead portion intervening between the electrode portion and the positive electrode collector plate or the negative electrode collector plate, and that the positioning holes are formed on the lead portion.
It is preferable in the first electrode plate unit that each of the positive electrode plate and the negative electrode plate is provided with a plurality of positioning holes, and at least one of the positioning holes has a circular shape and at least another positioning hole has an slot shape.
It is preferable in the first electrode plate unit that the positive electrode plate or the negative electrode plate is enveloped by the separator with the edge portion connected to the positive electrode collector plate or the negative electrode collector plate exposed. According to this preferable embodiment, short circuits between the positive electrode plate and the negative electrode plate can be suppressed more sufficiently.
In order to achieve the first object, a second electrode plate unit of the present invention includes a belt-like group of electrode plates in which a positive electrode plate and negative electrode plate that are laminated via a separator is rolled along the direction of the longer side, and the edge portion of the positive electrode plate protrudes from the edge portion of the negative electrode plate at least on a side face of the shorter side of the group of electrode plates. Here, xe2x80x9cthe shorter sidexe2x80x9d corresponds to the side parallel to the axial direction of the battery.
Also with such an electrode plate unit, it is possible to suppress the short circuit between the positive electrode and the negative electrode.
In order to achieve the second object, a third electrode plate unit includes a group of electrode plates in which a plurality of positive electrode plates and a plurality of negative electrode plates are laminated alternately via separators, and a collector plate connected to one side face of the group of electrode plates by a plurality of welding portions, wherein the interval between welding portions in the connection portion between the collector plate and the group of electrode plates is set to be narrower in the region in which the density of electric current collected by the collector plate is higher.
When a collector plate is provided so as to cover the side face of the group of electrode plates, the variation in the collecting density in the collector plate tends to be increased. In the portion in which the collecting density is high, the connecting portion between the collector plate and the group of electrode plates is subjected to a great thermal stress, and the connection tends to be fractured. However, with the third electrode plate unit, since welding portions are provided with high density in the portion where the collecting density is high so that the connecting strength and the collecting efficiency are enhanced, it is possible to improve the reliability with respect to the collecting effect of the collector plate.
Moreover, the xe2x80x9ccollecting densityxe2x80x9d denotes a current running in a unit cross-sectional area of the collector plate. In a case where the collector plate is connected to the group of electrode plates so as to cover the entire surface of the side face of the group of electrode plates, in a region closer to the external terminal, the collecting density of the collector plate is higher.
The third electrode plate unit can have, for example, a structure in which the collector plate is disposed with one end portion protruded from the group of electrode plates, and the welding portion is formed so that the intervals between the welding portions are narrower in a region closer to the edge portion of the collector plate being protruded from the group of the electrode plates.
In the structure in which the end portion of the collector plate is protruded from the group of electrode plates, the end portion is allowed to function as a connecting portion for electrically connecting the collector plate to the other components of the battery (for example, an external terminal, etc.). In this case, the collecting density is increased in a region closer to the end portion of the collector plate. Therefore, in order to enhance the connection strength and the collecting efficiency, by providing the welding portions with a high density in the region closer to the end portion of the collector plate, it is possible to improve the connection reliability of the collector plate.
In order to achieve the second object, a fourth electrode plate unit includes a group of electrode plates in which a plurality of positive electrode plates and a plurality of negative electrode plates are laminated alternately via separators, and a collector plate connected to one side face of the group of electrode plates by a plurality of welding portions, wherein a positioning hole is formed on the edge portion of each of the electrode plates being connected to the collector plate, and in the connecting surface between the collector plate and the group of electrode plates, the welding portion is formed so that the welding portion is not aligned with the positioning hole.
When the collector plate is connected to the group of electrode plates by aligning the edge portions of each electrode plate precisely on the side face on which the group of electrode plates and the collector plate are connected, it is possible to improve the connection strength and the reliability of the connection between the group of the electrode plates and the collector plate. According to the fourth electrode plate unit, since each electrode plate is provided with positioning holes, by inserting the pins into the positioning holes, it is possible to align the edge portions of the electrode plates. As a result, it is possible to improve the connection strength and the reliability of the connection between the group of the electrode plates and the collector plate.
However, if the positioning holes are formed on the electrode plate, the strength of the portion on which the positioning holes are formed is smaller than that of the other places. Therefore, it is thought to tend to be deformed or fractured due to heat when the collector plate is welded. The deformation or fracture of the electrode plate may cause the deterioration of the connection strength and reliability of the connection. However, according to the fourth electrode plate unit, the welding portion is formed on the portion excluding the portion on which the positioning holes are formed, and it is possible to suppress the deterioration of the connecting strength and the reliability of the connection between the collector plate and the group of electrode plates.
It is preferable in the fourth electrode plate unit that each of the electrode plates comprises an electrode portion filled with an active material and a lead portion intervening between the electrode portion and the electrode collector plate, and the positioning holes are formed on the lead portion.
It is preferable in the fourth electrode plate unit that a plurality of positioning holes are formed on each of the positive electrode plate and the negative electrode plate, and at least one of the positioning holes has a circular shape and at least another of the positioning holes has an slot shape.
Furthermore, it is preferable in the third and fourth electrode plate unit that the welding portion is of a linear shape along the direction in which the plates are laminated. According to this preferable embodiment, the strength and the reliability of the connection between the collector plate and the group of electrode plates further can be improved.
Furthermore, it is preferable in the third and fourth electrode plate units that a brazing filler metal is disposed between the collector plate and the group of electrode plates in the welding portion. According to this preferable embodiment, since the brazing filler metal is melted at a relatively low temperature, the strength and the reliability of the connection between the collector plate and the group of electrode plates further can be improved.
Furthermore, the present invention provides a battery wherein the electrode plate unit of any of the first to fourth electrode plate units is housed in a battery case together with the electrolyte.